Texas Congressman Ron Paul has won the straw poll at the annual Conservative Political Action Conference (CPAC) in Washington DC.
Mr Paul, who won last year, came ahead of former Massachusetts Governor Mitt Romney, who finished second.
The Texas lawmaker received 30% of votes cast by those attending, compared to Mr Romney's 23%. Others were grouped far behind.
CPAC is the Republican party's biggest annual convention.
The summit is an opportunity for possible candidates in the 2012 presidential election to test the waters and attract funding and support.
Although it is less than a year before the first voting in primaries for the 2012 race, no Republican has formally announced his or her candidacy. Correspondents say it is an unusually slow start to the campaign.
Mr Paul, a libertarian Republican with a loyal following, ran in GOP primaries in 2008.
As the results were announced in the hotel ballroom, cheers and boos broke out simultaneously, Reuters news agency reported.
The next highest contenders were former New Mexico Governor Gary Johnson and New Jersey Governor Chris Christie, who both received 6%, while former House Speaker Newt Gingrich won 5%.
Former Alaska Governor Sarah Palin finished a distant 9th place, garnering only 3% of the vote.
Ms Palin did not attend the summit, citing a scheduling conflict.
Straw polls are an indicator of the political temperature of those at the conference, but do not always match the outcome of presidential primaries.
Earlier in the conference, celebrity mogul Donald Trump told the gathering he would decide by June if he was running for president.
In the 2010 straw poll, Mr Paul won 31%, Mr Romney 22% and Ms Palin came third with 7%.